L08: Intorduction Of Viruses Flashcards
What scheme is used to classify viruses
Baltimore scheme
What does the baltimore scheme classify viruses depending on
Rna or dna
Double strand or single strand
Is there a reverse transcriptase
Sense (like mRNA) or antisense
How many groups are there in the Baltimore scheme
7
What is group 1
Double stranded DNA
What is group 2
Single stranded DNA
What is group 3
Double stranded rna
What is group 4
Sense RNA
What is group 5
Antisense RNA
What is group 6
RNA reverse transcribing
What is group 7
DNA reverse transcribing
Describe the viral life cycle
1) virus glycoproteins interact with the cells surface receptor
2) this enables receptor mediated endocytoses so virus enters cytoplasm
3) virus capsid with genetic material is transported to the cells nucleus
4) nucleic acids become, transcribed, transplanted, replication.
5) envelopment of genome
5) new protein/virus becomes assembled and released out of the cell.
Why is it important to know every stage of virus replication
So we can target it by drugs against them
What are drug target for viruses
Virion uncoating DNA polymerase Reverse transcriptase Viral protease Viral neuraminidase Inositol monophospahte dehydrogenase
What are the most clinically important viruses
Influenza virus
Hepatitis b and c
HIV
Herpes virus
What are the features of influenza
Enveloped
With glycoproteins of haemaglutinin and neuraminidase
Single RNA genome
What are the 3 types of influenza that infect humans
Influenza a: cause pandemic
Influenza b: cause seasonal epidemics
Influenza c: cause mild respiratory illness
What is influenza virus divided into subtypes depending on
Haemoglutinin or neuraminidase
What receptor does the haemagglutinin interact with in the airway epithelium
Alpha 2,6 Sialic acid
Why does influenza of haemaglutinin give repeated infections
Neutralising antibodies that stop haemooglutinin from binding to alpha 2,6 sialic acid stops working due to antigenic variation
What are the 2 types of antigenic variations
Antigenic shift
Antigenic drift
What is an antigenic drift
1) Small changes in the genes of influenza that happen continuously
2) the viruses accumulate overtime and generate proteins that have haemolgutinin mutated so neutralising antibodies do not recognise it
3) influenza therefore enters cells.
Why do mutations of virus genes occurs
Rna viruses have to replicate its RNA genome by RNA polymerase which lacks proofreading compared to DNA polymerase so they have greater mutations.
What is antigenic shift
This is not about mutation
A cell with 2 different viruses have there virus segments completely swapped
This results in a new virus.
How can antigenic shifts occur
Virus from birds get into pigs
Human influenza gets into pigs
What does antigenic shift cause
Pandemic
Which type influenza has antigenic shift occurs
Only in influenza a
What are the features of hepatitis b
Enveloped
DNA
Glycoproteins
E antigen expressed when the virus is replicating itself
How can hep b be transmitted
Perinatal transfusion Blood to blood Needle stick injury Sexual Medical instruments
Is hep b acute or chronic infections
Can start as acute but develop into chronic
How would you test for hep b
Test for antibodies
What will you see in an acute hep b infection in a test
HBe antigen during first exposure of virus
IgM antibodies after hep b exposure
What will you detect in chronic hep b infection
DNA
Hep b antigen hbe antigen
What is the features of hepatitis c
Enveloped
Single stranded RNA
Glycoproteins 1 and 2
How is hepatitis c transmitted
Blood borne e.g sharing injection equipment
Is hepatitis c infection acute or chronic
Starts as acute then can become chronic
How would you test for hepatitis c
Antibody testing to see if you have the infection before
If antibody test is positive you carry out viral nuclei acid test to tell you if you have a current infection
What does the test results show if you have had hep c but no current infection
Antibody positive
Rna negative
What would show if there is an acute infection
Antibody postive
Rna postive
Why do we get point mutation occuring for hepatitis c
Hepatitis c is a RNA virus so rna polymerase does not proofread which leads to point mutations
What does treatment to chronic hepatitis c depend on
Treatment depepends on genotype of hepatitis b
What is the structure of HIV
Enveloped
Rna single stranded
Glycoproteins : GP41 and GP120
Which immunity cells does HIV infect
CD4+ T cells
Macrophages
What are the subtypes of HIV
HIV-1
HIV-2
Does HIV involve acute or chronic infection
Chronic infection
Why do people with HIV get chronically infected
HIV replicated of low levels for decades
Virus loads increase as CD4+ T cell count drops
What happens when the person with HIV has a CD4+ T cell count below 200cell per mom
Person is diagnosed with AIDS
What is the maximal survival with someone with aids
3 years
Why is the maximum survival really low for AIDS
The person does not have immunity so they a prone to infections
Which infections are opportunistic in AIDS
Cryptococcal meningitis Toxoplasmosis Pneumocystis pneumonia Oesophageal candidiasis Certain cancers
How doe we test for HIV in the lab
HIV antibody test
If postive for antibody: nucliec acid test (measures virus load)
Antigen/antibody test: measures P24 antigen which is a marker of active virus replication
If HIV is an RNA virus what does this mean in terms of mutations
It is prone to mutations due to RNA polymerase not proofreading
What is the structure of herpes virus
Enveloped
Linear double stranded DNA
Glycoproteins
Has proteins inside which activate innate immunity
What are the 2 subtypes of herpes virus
HSV-1
HSV-2
What can HSV-1 cause
Stomatitis
What is stomatitis
Inflammation of mouth and lips
Why do you get stomatitis in HSV-1
Replication occurs in the mucoepithelial cells
What type of infection does herpes present with during later on in life
Latent infection
How does latency occur in herpes virus
Virus turns off its genes so the infected cells become immunologically silent
Reactivation of the virus can occur
Hsv1-/2 invade sensory neurones and establish latency in ganglia
If the virus invades the CNS what can this result in
Meningitis
What does varicella zoster virus cause
Chicken pox and shingles
Who gets chickenpox
Children
Who gets shingles
Elderly
What type of infection is shingles
Latent infection
